Although applicable to any number of micromechanical components and structures, particularly sensors and actuators, the present invention, as well as its basic underlying problem definition are explained with reference to a micromechanical air-quality sensor which can be manufactured using the technology of silicon surface micromechanics.
Existing air-quality sensors are implemented using a gas-sensitive material on a ceramic material. The gas-sensitive material changes its resistance and/or its dielectric properties in dependence upon the concentration of the gas to be detected. To obtain a good sensitivity, it is necessary to heat the gas-sensitive material. This disadvantageously entails the use of a ceramic material and the associated large type of design with respect to the substantial heating power to be expended and the long response time.
The method of etching silicon to make it porous (“anodizing”) constitutes related art, and it is described in numerous publications. The method of producing a cavity under a porous silicon layer is likewise already published (G. Lammel, P. Renaud, “Free-Standing Mobile 3D Microstructures of Porous Silicon”, Proceedings of the 13th European Conference on Solid-State Transducers, Eurosensors XIII, The Hague, 1999, 535-536).